As is known, most artificial or prosthetic arm and hand devices are clumsy, have severe motion limitations, and are unnatural in appearance. While remote manipulators similar to the forearm and hand have been used in space, planetary exploration, deep-sea work and in nuclear research, these suffer primarily from cost, controllability and an inability to reproduce human arm and hand motions. In this respect, most remote manipulators of the foregoing types, including the prosthetic devices, are unable to perform wrist motion in a compact mechanism. Designers have approached the problem along two separate lines. The first, and most common approach, is not to use wrist motion at all. This is most easily visualized by the "claw" or "hook" type of prosthetic. In the absence of wrist motion, the claw must be rotated about the axis of the arm to align the claw with the object to be grasped. This motion must be followed by orienting the arm such that the object picked up can be held at an acceptable angle relative to vertical.
Where size, weight and cost are not constraints and the degree of freedom provided by wrist motion is necessary, a gimbaled, azimuth/elevation type of wrist joint is used. However, only a two degree of freedom gimbaled wrist manipulator can duplicate the total wrist motion. Even if a two degree of freedom gimbaled arrangement is utilized, the required placement of the drive motors for the manipulator results in a rather large and bulky package.